The concept is great fun and it's fair to commend the writers, cast and crew for putting their hearts into a Star Trek musical.
I am not a big fan of musicals, but for me the songs are the highlight of this episode. They are pretty well written, performed, and choreographed, with all the cast getting an opportunity to shine.
It is a gimmick and there are moments where the novelty wears thin, but it builds to a feel-good finish that makes me smile. The theme of unity is very positive and one moment involving the Klingons is hilarious.
I am unsure how many of the cast are actually singing, but their body language and physical performances are all excellent. Jess Bush looks very comfortable doing these types of scenes and you would be forgiven for thinking her spectacular (for Star Trek) number is an actual music video.
The technobabble explanation for everything happening is silly, but no more so than numerous other explanations heard in the franchise for random events. Importantly the writers use the plot and songs to develop characters like Spock, Chapel, and Kirk in a way that links well to the original series.
Visually it excellent as always.
I can see, as always, reactions are either overly positive or full of hate-filled distain. For me the truth is rarely ever this extreme and is always in the eye of the beholder. My opinion is that it is a well made episode and I enjoyed it, but it is not up there with the very best of the franchise.
It's a 7.5/10 for me but I round upwards.